RE: What causes arrow fishtailing?
I agree, fletching contact with the rest is usually the cause of this problem, but the contact can be caused by torquing the bow. I suggest you powder test your rest, and arrow, setup to determine whether you are getting contact or not. Easton has a very good tuning guide on their web site that will explain arrow flight, and bow setup, far better than I could explain it here. I suggest you download it. Hope this helps. Be safe.
Shoot Straight
Derbytown